I. Field of the Invention
The present invention relates generally to a torque and angle sensor for a steering system.
II. Description of Related Art
In steering systems of the type used in automotive vehicles, the steering system typically includes an input shaft connected to the steering wheel. The input shaft is then connected to an output shaft through a torsion bar and the output shaft, in turn, is mechanically connected through linkage to the vehicle wheels. Consequently, rotation of the steering wheel pivots the wheels of the automotive vehicle through the torsion bar, output shaft, and steering linkage.
In many situations, it is highly desirable to determine the angular deflection between the input shaft and the output shaft of the steering mechanism. The degree of angular deflection between the input shaft and the output shaft, i.e. the angular deflection of the torsion bar, is then utilized by the vehicle management system to detect the applied steering wheel torque and then to determine the appropriate amount of assist provided by the power steering for the vehicle. For example, rotation of the vehicle if stopped or nearly stopped, e.g. a vehicle parking situation, typically creates a relatively high angular deflection between the input shaft and output shaft thus calling for increased power systems for turning the vehicle wheels. This deflection, furthermore, rarely exceeds 20 degrees.
Previously, inductive sensors have been used in connection with the steering mechanism to determine the angular deflection of the steering wheel torsion bar. In these previously known inductive sensors, a first conductive coupler is attached to one end of the torsion bar while a second conductive coupler is attached to the other end of the torsion bar. A PCB is then attached to the vehicle frame and positioned in between the two couplers.
The PCB has two sets of receiving coils. One set of receiving coils cooperates with the first coupler while, conversely, the second set of receiving coils operates in conjunction with the second coupler. Each receiving coil, furthermore, comprises a plurality of circumferentially adjacent, oppositely wound coils so that, when excited by a high frequency signal, the voltage output from each receiver coil will vary depending upon the angular position of its associated coupler.
One disadvantage of these previously known inductive sensors, however, is that the two inductive position sensors in the same area interfere with each other since they are both subjected to the same electromagnetic field. The output of each angular position sensor thus becomes a mixture of the signal from both positions of the couplers. In that event, it is difficult to extract the torsion angle from the two outputs from the receiver coils.
In order to minimize the interference between the two inductive sensors in the same area, there have been previously known attempts to differentiate the period of the two receiver coils. This, however, required additional computing resources since the mixed signals must be decoupled by certain algorithms.
In addition to the angular deflection between the input shaft and the output shaft of the steering mechanism, in many situations it is desirable to know the angular position of the vehicle wheels. Since the steering wheel typically can completely rotate multiple revolutions, it is necessary to keep track of the revolution count in order to determine the absolute angular position of the steering wheel and thus the absolute angular position of the vehicle wheels.